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Significant Accounting Policies (Narrative) (Details) (USD $)
12 Months Ended 3 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Significant Accounting Policies [Line Items]        
Canadian government securities with maturities greater than 90 days at the date of acquisition $ 461,313,000us-gaap_HeldToMaturitySecuritiesCurrent $ 374,842,000us-gaap_HeldToMaturitySecuritiesCurrent   $ 461,313,000us-gaap_HeldToMaturitySecuritiesCurrent
Maturity of Canadian government securities 90 days      
Impairment of assets 51,314,000us-gaap_ImpairmentOfOilAndGasProperties 21,587,000us-gaap_ImpairmentOfOilAndGasProperties 200,000,000us-gaap_ImpairmentOfOilAndGasProperties [1]  
Goodwill 0us-gaap_Goodwill 40,259,000us-gaap_Goodwill   0us-gaap_Goodwill
Stock Options [Member]        
Significant Accounting Policies [Line Items]        
Stock-based compensation, fair value assumption model Black-Scholes option pricing model      
Performance Based Restricted Stock [Member]        
Significant Accounting Policies [Line Items]        
Stock-based compensation, fair value assumption model Monte Carlo valuation model      
Stock-based compensation, vesting period 3 years      
Minimum [Member]        
Significant Accounting Policies [Line Items]        
Equity Method Investment, Ownership Percentage 20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
    20.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maturity of Canadian government securities   90 days    
Minimum [Member] | Stock Options [Member]        
Significant Accounting Policies [Line Items]        
Stock-based compensation, vesting period 2 years      
Maximum [Member]        
Significant Accounting Policies [Line Items]        
Equity Method Investment, Ownership Percentage 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
    50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Maximum [Member] | Stock Options [Member]        
Significant Accounting Policies [Line Items]        
Stock-based compensation, vesting period 3 years      
Natural Gas Processing Facilities [Member] | Minimum [Member]        
Significant Accounting Policies [Line Items]        
Depreciable lives, straight-line method 20 years      
Natural Gas Processing Facilities [Member] | Maximum [Member]        
Significant Accounting Policies [Line Items]        
Depreciable lives, straight-line method 25 years      
Syncrude [Member] | Minimum [Member]        
Significant Accounting Policies [Line Items]        
Turnarounds for major processing units 2 years      
Syncrude [Member] | Maximum [Member]        
Significant Accounting Policies [Line Items]        
Turnarounds for major processing units 3 years      
Canada [Member]        
Significant Accounting Policies [Line Items]        
Impairment of assets       $ 37,047,000us-gaap_ImpairmentOfOilAndGasProperties
/ us-gaap_StatementGeographicalAxis
= country_CA
[1] Results exclude corporate overhead, interest and discontinued operations.